<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style >
			.p2.p1{
				color: red;
			}
			.p1.p3{
				color: blue;
			}
			
		</style>
	</head>
	<body>
		<!-- 6、交集选择器 -->
		<h3 >这是标题</h3>
		<p class="p1 p2">这是标题</p>
		<p class=" p2 p3">这是标题</p>
		<p class="p1 p2 p3 ">这是标题</p>
		<h3 class="p1 p3">这是标题</h3>
	</body>
</html>
